1. Field of the Invention
The present invention relates to devices that automatically supply water to a steam boiler when the water level is low. More specifically, the present invention relates to water feeders for steam boilers of the type used in residential and light commercial heating applications that include a low water cutoff sensor to turn off the burner when the water is below the sensor.
2. Description of Related Art
In conventional boilers of the type used in residential and light commercial heating the water level is monitored with a low water cutoff sensor. When the water level in the boiler drops below the level of the low water cutoff sensor, the burner is turned off until the water level is brought back up to a safe level.
One method of adding water to this type of steam boiler is with an automatic water feeder, which controls a feed valve to supply water to the boiler. When the cutoff sensor senses a low water condition, it stops the burner from firing, and transfers power to the water feeder, allowing it to add make-up water. When the low water cutoff sensor detects that the water level has reached a safe level, it transfers power back to the burner, allowing it to restart and correspondingly disables the water feeder by removing its power.
In conventional water feeder designs of this type, the water feeder is disabled by the low water cutoff sensor as a result of the transfer of power away from the feeder to the burner. Thus the water feeder cannot feed water to the boiler after the burner is re-enabled. One type of low water cutoff sensor uses a float in the boiler, which mechanically drives a switch to transfer power between the burner and the water feeder. In this type of design, the power transfer occurs instantly, as the water level reaches a height sufficient for the float to operate the switch.
Another type low water cutoff sensor uses an electronic probe. With a probe-type electronic sensor, the transfer of power back to the burner can be delayed slightly, allowing a limited amount of additional water to be added above the probe level. However, because the same low water cutoff probe may be used on boilers of various sizes, this delay cannot be too long, as the water feeder cannot be allowed to feed an excess of water into a small boiler.
Water feeders currently available incorporate two timing circuits. The first timer (delay timer) provides for a delay period before the feed valve is activated. This delay allows time for steam within the heating system to condense to water and return to the boiler—thus ensuring that make-up water is required. If the low water cutoff sensor detects that the water level has returned to a safe operating level during the delay period, then no additional water is added and the cutoff sensor re-enables the burner allowing the boiler to operate normally.
The second timer (feed timer) controls the feed valve and adjusts the maximum time that the feeder will supply water to the boiler. After the delay timer has timed out, it triggers the feed timer, which operates the feed valve and begins supplying water to the boiler. When the water in the boiler reaches the low water cutoff sensor, the burner is re-enabled, the feed valve is turned off and the cycle repeats. The feed timer limits the maximum time that water feeding can occur during a feed cycle. Adjustable settings are provided on water feeders to accommodate boilers with different designs and different feed requirements. The best current water feeder designs also include a manual feed override to manually fill the boiler and a lockout feature to prevent the water feeder from cycling/feeding indefinitely in the event of a malfunction of the low water cut-off sensor.
One significant problem with current water feeder designs is that they provide no means for determining how much water has been added to a boiler. Introducing tap water to a boiler too frequently can shorten the life of the boiler. Over time, oxygen rich tap water can rust a cast iron boiler at the water line. Additionally, unwanted and potentially harmful elements, such as lime, can enter the boiler during each feed cycle. If there is a leak in the system, excess deposits can build up in the boiler and produce a layer of material at the bottom of the boiler. This layer typically has poor heat transfer characteristics and can result in the boiler cracking during heating. A water feeder having a display of the amount of water supplied by the water feeder is desirable to allow the owner or installer to determine if the boiler is operating normally, with normal water losses, or if water is leaking from the system, producing rapid water loss.
Another problem with current water feeder designs resides in the fact that the water feeder receives its power from the low water cutoff sensor, which transfers power from the burner to the feeder when the water level is low and removes power from the water feeder as soon as the water level reaches the cutoff sensor. In this type of design the low water cutoff sensor will stop the water feeder during the feed cycle when the level of the water is at or near the level of the cutoff sensor.
Regardless of the duration of the feed timer, the feeder can only fill to approximately the level of the cutoff sensor. While the low water cutoff sensor is installed in the boiler at a safe operating level, it is generally well below the optimum water level for operating the boiler. As a result, boiler operation with a conventional water feeder installed is less efficient than if the boiler were manually filled to operate at a higher water level in accordance with the manufacturer's recommendations.
One solution to this problem has been to use an upper water level sensor to determine when the water feeder has supplied enough water to reach the upper sensor level. The upper sensor is installed above the optimum water level. However, because an upper sensor must be installed at the time the boiler is constructed, and such a sensor increases costs, most boiler manufacturers do not install such a sensor. Consequently, this solution is not suitable for existing boiler installations.
To alleviate this problem installers in the field have made modifications to conventional water feeders by mounting a latching relay near to the water feeder and rewiring the connection between the low water cutoff sensor and the power wiring to the water feeder. The latching relay is installed to supply power to the water feeder after the low water cutoff sensor is satisfied and after the cutoff sensor attempts to remove power from the feeder. This field modification allows the feeder to complete a full feed timer cycle every time and bring the water level above the cutoff sensor. However, field modifications of existing designs are inconvenient at best and require additional installation work. An integrated water feeder design capable of supplying water to above the level of the low water cutoff sensor is desired by the industry.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a water feeder controller for a boiler having a display for indicating the quantity of water supplied by the water feeder to the boiler.
It is another object of the present invention to provide a water feeder controller for a boiler in which the water feeder raises the water level in the boiler well above the low water cutoff level during the fill cycle and completes an entire predetermined feed cycle during each feed period to add a known quantity of water to the boiler each cycle.
A further object of the invention is to provide a water feeder controller for a boiler that can fill well above the level of the low water cutoff sensor, without requiring a second sensor to detect a water level above the low water cutoff sensor.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.